The production of a good green colored signal has long been the nemesis of the pyrotechnician, particularly if a good green signal is defined as one with not only good color but also one that has a large luminous efficiency.
One standard Navy green flare has a typical output of dominant wavelength of 562 nm, an excitation purity of 53 percent of luminous power of 20,000 cd, a burn time of about 29 seconds, and a luminous efficiency of 4300 cd-s/g. The standard Navy green flare is composed of magnesium, potassium perchlorate, barium nitrate, a chlorine donor, such as polyvinyl chloride, other color additives, such as copper, and a binder. Various attempts have been made to improve on the standard Navy green flare and, heretofore, flares with better color can be obtained only with a large loss in luminous efficiency.
The magnitude of the problem of making a good green flare is illustrated in work performed under an Air Force contract by the Thiokol Chemical Corporation, and reported in Technical Report AFATL-TR-73-199, dated September 1973. This report states that,
" . . . a green smoke was obtained using small scale mixes in the laboratory, but scaled-up versions of these compositions when burned outdoors rapidly faded to white or bluish white clouds. A green flame, along with a green smoke, was never obtained with any of the test compositions." PA1 "The addition of barium perchlorate to the cobalt composition generally produced poorer quality smoke than potassium perchlorate. A green flame was not obtained in any of the cobalt compositions even when the amount of barium perchlorate was increased to 45 percent and the binder eliminated. The additon of copper to the compositions had no effect upon flame color which was not unexpected since the green flame from both the copper and barium halide flames are easily masked by other emitters in the flame. The addition of triethyl borate to the cobalt compositions, either alone or with the chlorinated polyester binder, resulted in orange-colored flames when the samples were burned in long grains. The high temperature of the sustained combustion zone apparently decomposed the oxyalkyl radicals which normally combine with the boron from the green emitting species."
This report further stated,